- ID:
- ivo://CDS.VizieR/J/ApJ/808/185
- Title:
- NuSTAR surveys: COSMOS catalog
- Short Name:
- J/ApJ/808/185
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To provide the census of the sources contributing to the X-ray background peak above 10keV, Nuclear Spectroscopic Telescope Array (NuSTAR) is performing extragalactic surveys using a three-tier "wedding cake" approach. We present the NuSTAR survey of the COSMOS field, the medium sensitivity, and medium area tier, covering 1.7deg^2^ and overlapping with both Chandra and XMM-Newton data. This survey consists of 121 observations for a total exposure of ~3Ms. To fully exploit these data, we developed a new detection strategy, carefully tested through extensive simulations. The survey sensitivity at 20% completeness is 5.9, 2.9, and 6.4x10^-14^erg/cm^2^/s in the 3-24, 3-8, and 8-24keV bands, respectively. By combining detections in 3 bands, we have a sample of 91 NuSTAR sources with 10^42^-10^45.5^erg/cm^2^/s luminosities and redshift z=0.04-2.5. Thirty-two sources are detected in the 8-24keV band with fluxes ~100 times fainter than sources detected by Swift-BAT. Of the 91 detections, all but 4 are associated with a Chandra and/or XMM-Newton point-like counterpart. One source is associated with an extended lower energy X-ray source. We present the X-ray (hardness ratio and luminosity) and optical-to-X-ray properties. The observed fraction of candidate Compton-thick active galactic nuclei measured from the hardness ratio is between 13%-20%. We discuss the spectral properties of NuSTAR J100259+0220.6 (ID 330) at z=0.044, with the highest hardness ratio in the entire sample. The measured column density exceeds 10^24^/cm2, implying the source is Compton-thick. This source was not previously recognized as such without the >10keV data.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/808/184
- Title:
- NuSTAR surveys: ECDF-S catalog
- Short Name:
- J/ApJ/808/184
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the initial results and the source catalog from the Nuclear Spectroscopic Telescope Array (NuSTAR) survey of the Extended Chandra Deep Field South (hereafter, ECDFS) --currently the deepest contiguous component of the NuSTAR extragalactic survey program. The survey covers the full ~30'x30' area of this field to a maximum depth of ~360ks (~220ks when corrected for vignetting at 3-24keV), reaching sensitivity limits of ~1.3x10^-14^erg/s/cm^2^ (3-8keV), ~3.4x10^-14^erg/s/cm^2^ (8-24keV), and ~3.0x10^-14^erg/s/cm^2^ (3-24keV). A total of 54 sources are detected over the full field, although five of these are found to lie below our significance threshold once contaminating flux from neighboring (i.e., blended) sources is taken into account. Of the remaining 49 that are significant, 19 are detected in the 8-24keV band. The 8-24 to 3-8keV band ratios of the 12 sources that are detected in both bands span the range 0.39-1.7, corresponding to a photon index range of {Gamma}~0.5-2.3, with a median photon index of {Gamma}{bar}=1.70+/-0.52. The redshifts of the 49 sources in our main sample span the range z=0.21-2.7, and their rest-frame 10-40keV luminosities (derived from the observed 8-24keV fluxes) span the range L_10-40keV_~(0.7-300)x10^43^erg/s, sampling below the "knee" of the X-ray luminosity function out to z~0.8-1. Finally, we identify one NuSTAR source that has neither a Chandra nor an XMM-Newton counterpart, but that shows evidence of nuclear activity at infrared wavelengths and thus may represent a genuine, new X-ray source detected by NuSTAR in the ECDFS.
- ID:
- ivo://CDS.VizieR/J/other/A+C/25.176
- Title:
- NVSS and FIRST variable sources
- Short Name:
- J/other/A+C/25.1
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In the present study we have cross-correlated NVSS and FIRST radio catalogues having radio flux measurements at the same 1.4GHz frequency. This way we benefit from repeated observations from both catalogues, as they give more accurate positions and fluxes and more important, reveal large differences between the two measured fluxes, thus allowing to establish radio variability. As a result 79382 radio variables have been revealed, including 6301 with flux differences at 1.4GHz larger than 15mJy, 1917 with flux differences 45mJy and 260 with flux differences 200mJy. By using a special technique (Mickaelian & Sinamyan 2010 (J/MNRAS/407/681) Mickaelian+ 2011 (J/MNRAS/415/1061)), 2425 optically variable objects out of 6301 radio sources have been revealed. 2425 radio sources with both high radio and optical variability into four categories have been divided. 1206 (19%) out of 6301 radio sources have activity types from available catalogues and 619 (25.5%) out of 2425 radio sources with at the same time radio and optical variability have activity types from available catalogues. In addition, 279 radio sources out of 2425 have high variability in optical range. We have established their activity types when available. The IR fluxes and colours for the 6301 variable radio sources have been studied. Colour-colour diagrams show that most of the "unknown" sources are galaxies. The activity types for 110 (42%) out of 260 extremely high variable radio sources also have been retrieved.
- ID:
- ivo://CDS.VizieR/J/ApJ/813/42
- Title:
- O and B type stars in W3: first results
- Short Name:
- J/ApJ/813/42
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first results from our survey of the star-forming complex W3, combining VRI photometry with multiobject spectroscopy to identify and characterize the high-mass stellar population across the region. With 79 new spectral classifications, we bring the total number of spectroscopically confirmed O- and B-type stars in W3 to 105. We find that the high-mass slope of the mass function in W3 is consistent with a Salpeter IMF, and that the extinction toward the region is best characterized by an R_V_ of approximately 3.6. B-type stars are found to be more widely dispersed across the W3 giant molecular cloud (GMC) than previously realized: they are not confined to the high-density layer (HDL) created by the expansion of the neighboring W4 H ii region into the GMC. This broader B-type population suggests that star formation in W3 began spontaneously up to 8-10 Myr ago, although at a lower level than the more recent star formation episodes in the HDL. In addition, we describe a method of optimizing sky subtraction for fiber spectra in regions of strong and spatially variable nebular emission.
- ID:
- ivo://CDS.VizieR/J/ApJ/814/11
- Title:
- Obscured AGNs from XMM-Newton and AKARI
- Short Name:
- J/ApJ/814/11
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report a new sample of obscured active galactic nuclei (AGNs) selected from the XMM-Newton serendipitous source and AKARI point-source catalogs. We match X-ray sources with infrared (18 and 90{mu}m) sources located at |b|>10{deg} to create a sample consisting of 173 objects. Their optical classifications and absorption column densities measured by X-ray spectra are compiled and study efficient selection criteria to find obscured AGNs. We apply the criteria (1) X-ray hardness ratio defined by using the 2-4.5keV and 4.5-12keV bands >-0.1 and (2) EPIC-PN count rate (CR) in the 0.2-12keV to infrared flux ratio CR/F_90_<0.1 or CR/F_18_<1 where F_18_ and F_90_ are infrared fluxes at 18 and 90{mu}m in Jy, respectively, to search for obscured AGNs. X-ray spectra of 48 candidates, for which no X-ray results have been published, are analyzed and X-ray evidence for the presence of obscured AGNs such as a convex shape X-ray spectrum indicative of absorption of N_H_~10^22-24^/cm2, a very flat continuum, or a strong Fe-K emission line with an equivalent width of >700eV is found in 26 objects. Six of them are classified as Compton-thick AGNs, and four are represented by either Compton-thin or Compton-thick spectral models. The success rate of finding obscured AGNs combining our analysis and the literature is 92% if the 18{mu}m condition is used. Of the 26 objects, 4 are optically classified as an HII nucleus and are new "elusive AGNs" in which star formation activity likely overwhelms AGN emission in the optical and infrared bands.
- ID:
- ivo://CDS.VizieR/J/ApJ/687/471
- Title:
- Observational comparison between ULXs and XRBs
- Short Name:
- J/ApJ/687/471
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- To test the idea that ultraluminous X-ray sources (ULXs) in external galaxies represent a class of accreting intermediate-mass black holes (IMBHs), we have undertaken a program to identify ULXs and a lower luminosity X-ray comparison sample with the highest quality data in the Chandra archive. We establish as a general property of ULXs that the most X-ray-luminous objects possess the flattest X-ray spectra (in the Chandra bandpass). No prior sample studies have established the general hardening of ULX spectra with luminosity. This hardening occurs at the highest luminosities (absorbed luminosity >=5x10^39^erg/s) and is in line with recent models arguing that ULXs are actually stellar mass black holes. From spectral modeling, we show that the evidence originally taken to mean that ULXs are IMBHs - i.e., the "simple IMBH model" - is nowhere near as compelling when a large sample of ULXs is looked at properly. During the last couple of years, XMM-Newton spectroscopy of ULXs has to a large extent begun to negate the simple IMBH model based on fewer objects. We confirm and expand these results, which validates the XMM-Newton work in a broader sense with independent X-ray data.
- ID:
- ivo://CDS.VizieR/III/6
- Title:
- OB stars in Milky Way
- Short Name:
- III/6
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- (no description available)
- ID:
- ivo://CDS.VizieR/J/AJ/143/52
- Title:
- Old star clusters in NGC 4449 from HST imaging
- Short Name:
- J/AJ/143/52
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use Hubble Space Telescope imaging to show that the nearby dwarf starburst galaxy NGC 4449 (=UGC 7592) has an unusual abundance of luminous red star clusters. Joint constraints from integrated photometry, low-resolution spectroscopy, dynamical mass-to-light ratios, and resolved color-magnitude diagrams provide evidence that some of these clusters are old globular clusters (GCs). Spectroscopic data for two massive clusters suggest intermediate metallicities ([Fe/H]~-1) and subsolar Mg enhancement ([Mg/Fe]~-0.1 to -0.2). One of these clusters may be the nucleus of a tidally disrupting dwarf galaxy; the other is very massive (~3*10^6^M_{sun}_). We have also identified a population of remote halo GCs. NGC 4449 is consistent with an emerging picture of the ubiquity of stellar halos among dwarf galaxies, and study of its GCs may help distinguish between accretion and in situ scenarios for such halos.
- ID:
- ivo://CDS.VizieR/J/A+A/561/A93
- Title:
- On the metallicity of open clusters. II.
- Short Name:
- J/A+A/561/A93
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The literature was searched for [Fe/H] estimates of individual member stars of open clusters (OCs) based on the analysis of high-resolution spectra. The lower limit for spectral resolving power (R={lambda}/{Delta}{lambda}) was set to 25000, and the lower limit for signal-to-noise ratio was set to 50. We searched the PASTEL database (2010A&A...515A.111S, Cat. B/pastel) and the recent literature for such metallicity determinations in references posterior to 1990 and until June 2013. Only stars with an effective temperature lower than 7000K were included to avoid rapid rotators and chemical peculiarities. We eliminated confirmed non-members, spectroscopic binaries, and chemically peculiar stars and kept only stars with a high probability of membership. This resulted in a list of 571 stars in 86 OCs, with 830 metallicity determinations from 94 papers, which we call the starting sample.
- ID:
- ivo://CDS.VizieR/J/A+A/575/A42
- Title:
- Optical counterparts of ROSAT X-ray in 2 fields
- Short Name:
- J/A+A/575/A42
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The optical identification of large number of X-ray sources such as those from the ROSAT All-Sky Survey is challenging with conventional spectroscopic follow-up observations. We investigate two ROSAT All-Sky Survey fields of size 10{deg}x10{deg} each, one at galactic latitude b=83{deg} (26 Com), the other at b=-5{deg} (gamma Sge), in order to optically identify the majority of sources. We used optical variability, among other more standard methods, as a means of identifying a large number of ROSAT All- Sky Survey sources. All objects fainter than about 12mag and brighter than about 17mag, in or near the error circle of the ROSAT positions, were tested for optical variability on hundreds of archival plates of the Sonneberg field patrol.
